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Unread 04-05-2012, 13:03
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Re: Non-FRC Motor Controller?


For the forward direction, Q3 is always off and Q4 is always on. So for a single-direction drive you could remove Q3 and replace Q4 with a shunt.

During the ON portion of the output PWM cycle, Q1 is ON and Q2 is OFF.

During the OFF portion of the output PWM cycle, Q1 is OFF and Q2 is ON.

Q1 and Q2 must never be ON at the same time (I think you can see why). Thus, there is always a slight "dead time" where both Q1 and Q2 are OFF when switching states. During this dead time, the intrinsic diode in Q2 allows the inductive current in the motor to continue flowing so it doesn't create a large voltage spike.

So, during the OFF portion of the output PWM cycle, the stored energy in the motor's coils causes current to continue flowing through Q2 and Q4. This current maintains the motor's torque during the OFF portion.